The overall aim of this study is to investigate the biology of the Mycoplasmatales and to elucidate the mechanisms of pathogenesis of the diseases with which they are associated. Detailed investigations on experimental murine arthritis are designed to provide a model which will enhance understanding of the pathogenesis and etiology of human rheumatoid arthritis. Host parasite relationships are being studied in regard to humoral and cellular antibody response, nature of chronicity of disease and role of toxins. A search is being conducted 1) for an infectious agent isolable from human rheumatoid synovium, and 2) for humoral and cell bound antibodies against mycoplasmas in human rheumatoid and non-rheumatoid sera. Characterization of new mycoplasma isolates is continuing.